Abstract

Most of the previous studies on nanosecond (ns) laser-induced plasma typically use relatively short ns laser pulses (pulse duration less than to 50 ns). In this paper, relatively long ns laser pulses with 200 ns duration have been used, and the produced plasma during metal ablation in air at atmospheric pressure has been studied through time-resolved observation using an intensified charge-coupled device camera. Due to the much longer ns laser pulse duration, the plasma radiation intensity distribution and the plasma front propagation have different physical features from those produced by much shorter ns laser pulses. In particular, it has been observed that during the laser pulse the plasma has two high-radiation-intensity regions: one is located right above the target surface while the other is behind the expanding plasma front. The former region will disappear once the laser pulse completes. This interesting physical phenomenon has been rarely reported, and requires further experimental and modeling study to completely understand.

Received 30 April 2010Accepted 18 September 2010Published online 02 November 2010

Acknowledgments:

This work was supported by General Atomics. Dr. Benxin Wu’s work supported by National Science Foundation (Award No. CMMI-0826184) was also very helpful to the work in this paper, which we also would like to acknowledge.